Process for Selectivating Catalyst for Producing Paraxylene by Methylation of Benzene and/or Toluene

ABSTRACT

A process is described for producing paraxylene, in which an aromatic hydrocarbon feedstock comprising benzene and/or toluene is contacted with an alkylating reagent comprising methanol and/or dimethyl ether in an alkylation reaction zone under alkylation conditions in the presence of an alkylation catalyst to produce an alkylated aromatic product comprising xylenes. The alkylation catalyst comprises a molecular sieve having a Constraint Index ≤5, and the alkylation conditions comprise a temperature less than 500° C. The alkylation catalyst may be selectivated to produce a higher than equilibrium amount of paraxylene by using a molar ratio of alkylating agent to aromatic of at least 1:4.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/405,036, filed Oct. 6, 2016 and U.S. ProvisionalPatent Application Ser. No. 62/437,493, filed Dec. 21, 2016, both ofwhich are hereby incorporated herein by reference in their entireties.

FIELD

This disclosure relates to a process for selectivating a catalyst forthe methylation of benzene and/or toluene to produce xylenes,particularly paraxylene.

BACKGROUND

Xylenes are valuable precursors in the chemical industry. Of the threexylene isomers, paraxylene is the most important since it is a startingmaterial for manufacturing terephthalic acid, which is itself a valuableintermediate in the production of synthetic polyester fibers, films, andresins. Currently, the demand for paraxylene is growing at an annualrate of 5-7%.

One known route for the manufacture of paraxylene is by the methylationof benzene and/or toluene. For example, U.S. Pat. No. 6,504,072discloses a process for the selective production of paraxylene whichcomprises reacting toluene with methanol under alkylation conditions inthe presence of a catalyst comprising a porous crystalline materialhaving a Diffusion Parameter for 2,2 dimethylbutane of about 0.1-15sec⁻¹ when measured at a temperature of 120° C. and a 2,2 dimethylbutanepressure of 60 torr (8 kPa). The porous crystalline material ispreferably a medium-pore zeolite, particularly ZSM-5, which has beenseverely steamed at a temperature of at least 950° C. The alkylationconditions include a temperature between about 500 and 700° C., apressure of between about 1 atmosphere and 1000 psig (100 and 7000 kPa),a weight hourly space velocity between about 0.5 and about 1000 and amolar ratio of toluene to methanol of at least about 0.2.

In addition, U.S. Pat. No. 6,642,426 discloses a process for alkylatingan aromatic hydrocarbon reactant, especially toluene, with an alkylatingreagent comprising methanol to produce an alkylated aromatic product,comprising: introducing the aromatic hydrocarbon reactant into a reactorsystem at a first location, wherein the reactor system includes afluidized bed reaction zone comprising a temperature of 500 to 700° C.and an operating bed density of about 300 to 600 kg/m³, for producingthe alkylated aromatic product; introducing a plurality of streams ofsaid alkylating reactant directly into said fluidized bed reaction zoneat positions spaced apart in the direction of flow of the aromatichydrocarbon reactant, at least one of said streams being introduced at asecond location downstream from the first location; and recovering thealkylate aromatic product, produced by reaction of the aromatic reactantand the alkylating reagent, from the reactor system. The preferredcatalyst is ZSM-5 which has been selectivated by high temperaturesteaming.

As exemplified by the U.S. Patents discussed above, current processesfor the alkylation of benzene and/or toluene with methanol are conductedat high temperatures, i.e., between 500 to 700° C. in the presence of amedium pore size zeolite, particularly ZSM-5. This results in a numberof problems, particularly in that catalyst life per cycle is relativelyshort and so frequent regeneration of the catalyst is required. Inaddition, the existing processes typically result in significantquantities of methanol being converted to ethylene and other lightolefins which reduces the yield of desirable products, such as xylenes,and increases recovery costs.

There is therefore a need for an improved process for the alkylation ofbenzene and/or toluene with methanol (or dimethyl ether), whichincreases the paraxylene selectivity of the catalyst and produces ahigher than equilibrium amount of paraxylene.

SUMMARY

Toluene and/or benzene may be converted to xylenes via an alkylationreaction with methanol and/or dimethyl ether conducted under relativelymild conditions, namely a temperature less than 500° C., in the presenceof an alkylation catalyst comprising a molecular sieve having aConstraint Index less than or equal to 5. The lower temperaturealkylation reaction produces less light gas by-products and achieveslonger catalyst cycle life than conventional high temperature processes.Methanol utilization (i.e., percentage of methanol converted toaromatics) is also improved as compared to conventional high temperatureprocesses.

To increase the concentration of paraxylene in the product mixture andobtain a higher than equilibrium concentration of paraxylene, thealkylation catalyst may be selectivated. In one embodiment, thealkylation catalyst is selectivated by using an alkylating agent toaromatic molar ratio of at least 1:4 until the target paraxyleneselectivity is reached. Once the target paraxylene selectivity isachieved, the molar ratio of alkylating agent to aromatic may bemaintained or decreased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of paraxylene selectivity against time on stream inthe process of alkylating toluene with methanol described in theExample.

FIG. 2 is a graph of toluene and methanol conversion against time onstream in the process of alkylating toluene with methanol described inthe Example.

FIG. 3 is a graph of xylenes selectivity against time on stream in theprocess of alkylating toluene with methanol described in the Example.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments disclosed herein provide alkylation processes for producingxylenes, particularly paraxylene, that can be conducted under relativelymild conditions to produce xylenes with less light gas by-products andlonger catalyst cycle life than conventional high temperature processes.Methanol utilization (i.e., percentage of methanol converted toaromatics) is also improved. In at least some embodiments, an aromatichydrocarbon feed comprising benzene and/or toluene is contacted with analkylating reagent comprising methanol and/or dimethyl ether in at leastone alkylation reaction zone in the presence of alkylation catalystunder alkylation conditions. The alkylation catalyst comprises amolecular sieve having a Constraint Index less than 5, such as less than4, for example less than 3, or in some embodiments less than 2, and thealkylation conditions comprise a temperature less than 500° C.

The process is effective to convert the benzene and/or toluene toxylenes with essentially 100% methanol conversion and substantially nolight gas make. The high methanol utilization is surprising in light ofthe methanol utilization in the prior art toluene and/or benzenemethylation processes, and results in the substantial advantages of lesscoke formation, which increases the catalyst life. Furthermore, in priorart processes, it is preferred to co-feed steam into the reactor withthe methanol to minimize the methanol side reactions, and the steamnegatively impacts catalyst life. With the nearly 100% of the methanolreacting with aromatic rings to produce aromatics in the inventiveprocess, there is no need to co-feed steam, decreasing the energydemands of the process and increasing catalyst life.

The methanol selectivity to xylenes in embodiments disclosed herein istypically on the order of 80%, with the main by-products being benzeneand C₉₊ aromatics. The benzene can be separated from the alkylationeffluent and recycled back to the alkylation reaction zone(s), while theC₉₊ aromatics can be separated for blending into the gasoline pool ortransalkylated with additional benzene and/or toluene to make additionalxylenes. The life of the alkylation catalyst is enhanced as comparedwith existing processes since methanol decomposition is much less at thelower reaction temperature. Moreover, the use of a larger pore molecularsieve minimizes diffusion limitations and allows the alkylation to becarried out at commercially viable WHSVs. Additionally, when a toluenefeed (one having at least 90 wt % of toluene) is used, more alkylatingagent reacts with the toluene, versus other molecules such as alkylatingagent or by-products of the reaction, to produce xylenes as compared toexisting processes.

The amount of paraxylene in the xylenes product can be increased up toat least 35 wt % by selectivating the alkylation catalyst. In oneembodiment, the alkylation catalyst is selectivated in-situ by using atleast a 1:4 alkylating agent to aromatic molar ratio in the feed. Afterthe desired paraxylene selectivity is achieved, the alkylating agent toaromatic ratio in the feed may be maintained or decreased for theremainder of the reaction. If the alkylating agent to aromatic ratio isdecreased after the catalyst has been selectivated, the alkylating agentto aromatic ratio may subsequently be raised to re-selectivate thecatalyst if the paraxylene selectivity of the catalyst decreases below apredetermined threshold.

As used herein, the term “C_(n)” hydrocarbon wherein n is a positiveinteger, e.g., 1, 2, 3, 4, 5, etc., means a hydrocarbon having n numberof carbon atom(s) per molecule. The term “C_(n+)” hydrocarbon wherein nis a positive integer, e.g., 1, 2, 3, 4, 5, etc., means a hydrocarbonhaving at least n number of carbon atom(s) per molecule. The term“C_(n−)” hydrocarbon wherein n is a positive integer, e.g., 1, 2, 3, 4,5, etc., as used herein, means a hydrocarbon having no more than nnumber of carbon atom(s) per molecule.

As used herein, the terms “alkylating” and “methylating”, or“alkylation” and “methylation” may be used interchangeably.

Constraint Index is a convenient measure of the extent to which amolecular sieve provides control of molecules of varying sizes to itsinternal structure. The method by which Constraint Index is determinedis described fully in U.S. Pat. No. 4,016,218, which is incorporatedhereby by reference for details of the method.

Examples of suitable molecular sieves having a Constraint Index lessthan 5 suitable for use in the present process comprise zeolite beta,zeolite Y, Ultrastable Y (USY), Ultrahydrophobic Y (UHP-Y), DealuminizedY (Deal Y), mordenite, ZSM-3, ZSM-4, ZSM-12, ZSM-14, ZSM-18, ZSM-20 andmixtures thereof. Zeolite ZSM-3 is described in U.S. Pat. No. 3,415,736.Zeolite ZSM-4 is described in U.S. Pat. No. 4,021,947. Zeolite ZSM-12 isdescribed in U.S. Pat. No. 3,832,449. Zeolite ZSM-14 is described inU.S. Pat. No. 3,923,636. Zeolite ZSM-18 is described in U.S. Pat. No.3,950,496. Zeolite ZSM-20 is described in U.S. Pat. No. 3,972,983.Zeolite Beta is described in U.S. Pat. No. 3,308,069, and Re. No.28,341. Low sodium Ultrastable Y molecular sieve (USY) is described inU.S. Pat. Nos. 3,293,192 and 3,449,070. Ultrahydrophobic Y (UHP-Y) isdescribed in U.S. Pat. No. 4,401,556. Dealuminized Y zeolite (Deal Y)may be prepared by the method found in U.S. Pat. No. 3,442,795. ZeoliteY and mordenite are naturally occurring materials but are also availablein synthetic forms, such as TEA-mordenite (i.e., synthetic mordeniteprepared from a reaction mixture comprising a tetraethylammoniumdirecting agent). TEA-mordenite is disclosed in U.S. Pat. Nos. 3,766,093and 3,894,104.

One preferred class of molecular sieve suitable for use in the presentprocess, and having a Constraint Index less than 5, are crystallinemicroporous materials of the MWW framework type. As used herein, theterm “crystalline microporous material of the MWW framework type”includes one or more of:

-   -   molecular sieves made from a common first degree crystalline        building block unit cell, which unit cell has the MWW framework        topology. (A unit cell is a spatial arrangement of atoms which        if tiled in three-dimensional space describes the crystal        structure. Such crystal structures are discussed in the “Atlas        of Zeolite Framework Types”, Fifth edition, 2001, the entire        content of which is incorporated as reference);    -   molecular sieves made from a common second degree building        block, being a 2-dimensional tiling of such MWW framework        topology unit cells, forming a monolayer of one unit cell        thickness, preferably one c-unit cell thickness;    -   molecular sieves made from common second degree building blocks,        being layers of one or more than one unit cell thickness,        wherein the layer of more than one unit cell thickness is made        from stacking, packing, or binding at least two monolayers of        MWW framework topology unit cells. The stacking of such second        degree building blocks can be in a regular fashion, an irregular        fashion, a random fashion, or any combination thereof; and    -   molecular sieves made by any regular or random 2-dimensional or        3-dimensional combination of unit cells having the MWW framework        topology.

Crystalline microporous materials of the MWW framework type includethose molecular sieves having an X-ray diffraction pattern includingd-spacing maxima at 12.4±0.25, 6.9±0.15, 3.57±0.07 and 3.42±0.07Angstrom. The X-ray diffraction data used to characterize the materialare obtained by standard techniques using the K-alpha doublet of copperas incident radiation and a diffractometer equipped with a scintillationcounter and associated computer as the collection system.

Examples of crystalline microporous materials of the MWW framework typeinclude MCM-22 (described in U.S. Pat. No. 4,954,325), PSH-3 (describedin U.S. Pat. No. 4,439,409), SSZ-25 (described in U.S. Pat. No.4,826,667), ERB-1 (described in European Patent No. 0293032), ITQ-1(described in U.S. Pat. No. 6,077,498), ITQ-2 (described inInternational Publication No. WO97/17290), MCM-36 (described in U.S.Pat. No. 5,250,277), MCM-49 (described in U.S. Pat. No. 5,236,575),MCM-56 (described in U.S. Pat. No. 5,362,697), UZM-8 (described in U.S.Pat. No. 6,756,030), UZM-8HS (described in U.S. Pat. No. 7,713,513),UZM-37 (described in U.S. Pat. No. 7,982,084), EMM-10 (described in U.S.Pat. No. 7,842,277), EMM-12 (described in U.S. Pat. No. 8,704,025),EMM-13 (described in U.S. Pat. No. 8,704,023), MIT-1 (described by Luoet. al, in Chemical Science, 2015, Vol. 6, pp. 6320-6324) and mixturesthereof, with MCM-49 generally being preferred.

In some embodiments, the crystalline microporous material of the MWWframework type employed herein may be contaminated with othercrystalline materials, such as ferrierite or quartz. These contaminantsmay be present in quantities ≤10% by weight, normally ≤5% by weight.

Additionally or alternatively, the molecular sieves useful herein may becharacterized by a ratio of silicon to aluminum. In particularembodiments, the molecular sieves suitable herein include those having aSi/Al ratio of less than 100, preferably about 15 to 50.

The molecular sieve catalyst may be selectivated to produce a higherthan equilibrium amount of paraxylene, that is more than about 23 wt %of paraxylene, based on the total amount of xylenes, in the productmixture. In one embodiment, the concentration of paraxylene in thexylene fraction is at least 35 wt %, preferably at least 40 wt %, andmore preferably at least 45 wt %. The selectivation of the catalyst maybe conducted in-situ by using a feed with an alkylating agent toaromatic ratio of at least 1:4, or 1:3, or 1:2 until the targetparaxylene selectivity is reached. As used herein, the target paraxyleneselectivity means at least 35 wt %, preferably at least 40 wt %, andmore preferably at least 45 wt % of paraxylene in the xylenes fraction.Once the target paraxylene selectivity is achieved, the alkylating agentto aromatic ratio of the feed may be decreased, though in someembodiments, the alkylating agent to aromatic ratio is maintained evenafter the target paraxylene selectivity is achieved. If the alkylatingagent to aromatic ratio is decreased once the catalyst is sufficientlyselectivated, and the paraxylene selectivity decreases below the targetparaxylene selectivity, the alkylating agent to aromatic ratio of thefeed may again be increased to re-selectivate the catalyst.

The catalyst may additionally or alternatively be selectivated, eitherbefore introduction into the aromatization reactor or in-situ in thereactor, by contacting the catalyst with a selectivating agent, such assilicon, steam, coke, or a combination thereof. In one embodiment, thecatalyst is silica-selectivated by contacting the catalyst with at leastone organosilicon in a liquid carrier and subsequently calcining thesilicon-containing catalyst in an oxygen-containing atmosphere, e.g.,air, at a temperature of 350 to 550° C. A suitable silica-selectivationprocedure is described in U.S. Pat. No. 5,476,823, the entire contentsof which are incorporated herein by reference. In another embodiment,the catalyst is selectivated by contacting the catalyst with steam.Steaming of the zeolite is effected at a temperature of at least about950° C., preferably about 950 to about 1075° C., and most preferablyabout 1000 to about 1050° C., for about 10 minutes to about 10 hours,preferably from 30 minutes to 5 hours. The selectivation procedure,which may be repeated multiple times, alters the diffusioncharacteristics of the molecular sieve and may increase the xyleneyield.

In addition to, or in place of, silica or steam selectivation, thecatalyst may be subjected to coke selectivation. This optional cokeselectivation typically involves contacting the catalyst with athermally decomposable organic compound at an elevated temperature inexcess of the decomposition temperature of said compound but below thetemperature at which the crystallinity of the molecular sieve isadversely affected. Further details regarding coke selectivationtechniques are provided in the U.S. Pat. No. 4,117,026, incorporated byreference herein. In some embodiments, a combination of silicaselectivation and coke selectivation may be employed.

It may be desirable to combine the molecular sieve, prior toselectivating, with at least one oxide modifier, such as at least oneoxide selected from elements of Groups 2 to 4 and 13 to 16 of thePeriodic Table. Most preferably, said at least one oxide modifier isselected from oxides of boron, magnesium, calcium, lanthanum, and mostpreferably phosphorus. In some cases, the molecular sieve may becombined with more than one oxide modifier, for example a combination ofphosphorus with calcium and/or magnesium, since in this way it may bepossible to reduce the steaming severity needed to achieve a targetdiffusivity value. In some embodiments, the total amount of oxidemodifier present in the catalyst, as measured on an elemental basis, maybe between about 0.05 and about 20 wt %, and preferably is between about0.1 and about 10 wt %, based on the weight of the final catalyst. Wherethe modifier includes phosphorus, incorporation of modifier into thecatalyst is conveniently achieved by the methods described in U.S. Pat.Nos. 4,356,338, 5,110,776, 5,231,064, and 5,348,643, the entiredisclosures of which are incorporated herein by reference.

The above molecular sieves may be used as the alkylation catalystemployed herein without any binder or matrix. Alternatively, themolecular sieves may be composited with another material which isresistant to the temperatures and other conditions employed in thealkylation reaction. Such materials include active and inactivematerials and synthetic or naturally occurring zeolites as well asinorganic materials such as clays and/or oxides such as alumina, silica,silica-alumina, zirconia, titania, magnesia or mixtures of these andother oxides. The latter may be either naturally occurring or in theform of gelatinous precipitates or gels including mixtures of silica andmetal oxides. Clays may also be included with the oxide type binders tomodify the mechanical properties of the catalyst or to assist in itsmanufacture. Use of a material in conjunction with the molecular sieve,i.e., combined therewith or present during its synthesis, which itselfis catalytically active may change the conversion and/or selectivity ofthe catalyst. Inactive materials suitably serve as diluents to controlthe amount of conversion so that products may be obtained economicallyand orderly without employing other means for controlling the rate ofreaction. These materials may be incorporated into naturally occurringclays, e.g., bentonite and kaolin, to improve the crush strength of thecatalyst under commercial operating conditions and function as bindersor matrices for the catalyst. The relative proportions of molecularsieve and inorganic oxide matrix vary widely, with the sieve contentranging from about 1 to about 90 wt % and more usually, particularly,when the composite is prepared in the form of beads, in the range ofabout 2 to about 80 wt % of the composite.

The feeds to the present process comprise an aromatic hydrocarbon feed,comprising benzene and/or toluene, and an alkylating reagent comprisingmethanol and/or dimethyl ether. Any refinery aromatic feed can be usedas the source of the benzene and/or toluene, although in someembodiments it may be desirable to use an aromatic hydrocarbon feedwhich comprises at least 90 wt % toluene. In addition, in someembodiments, it may be desirable to pre-treat the aromatic hydrocarbonfeed to remove catalyst poisons, such as nitrogen and sulfur-compounds.In other embodiments, the feed may further include non-aromatics, suchas a refinery aromatic feed from which the non-aromatics have not beenextracted.

The present alkylation process is conducted at relatively lowtemperatures, namely less than 500° C., such as less than 475° C., orless than 450° C., or less than 425° C., or less than 400° C. In orderto provide commercially viable reaction rates, the process may beconducted at temperatures of at least 250° C., such as least 275° C.,for example least 300° C. In terms of ranges, the process may beconducted at temperatures ranging from 250 to less than 500° C., such asfrom 275 to 475° C., for example from 300 to 450° C. Operating pressureswill vary with temperature but generally are at least 700 kPa-a, such asat least 1000 kPa-a, for example at least 1500 kPa-a, or at least 2000kPa-a, up to about 7000 kPa-a, for example up to about 6000 kPa-a, up toabout 5000 kPa-a. In terms of ranges, operating pressures may range from700 kPa-a to 7000 kPa-a, for example from 1000 kPa-a to 6000 kPa-a, suchas from 2000 kPa-a to 5000 kPa-a. Suitable WHSV values based on totalaromatic and alkylating reagent feeds are in the range from 50 to 0.5hr⁻¹, such as in the range from 10 to 1 hr⁻¹. In some embodiments, atleast part of the aromatic feed, the methanol alkylating reagent and/orthe alkylation effluent may be present in the alkylation reaction zonein the liquid phase.

The alkylation reaction can be conducted in any known reactor systemincluding, but not limited to, a fixed bed reactor, a moving bedreactor, a fluidized bed reactor and a reactive distillation unit. Inaddition, the reactor may comprise a single reaction zone or multiplereaction zones located in the same or different reaction vessels. Inaddition, injection of the methanol/dimethyl ether alkylating agent canbe effected at a single point in the reactor or at multiple pointsspaced along the reactor.

The product of the alkylation reaction comprises xylenes, benzene and/ortoluene (both residual and coproduced in the process), C₉₊ aromatichydrocarbons, co-produced water, oxygenate by-products, and in somecases, unreacted methanol. It is, however, generally preferred tooperate the process so that all the methanol is reacted with thearomatic hydrocarbon feed and the alkylation product is generally freeof residual methanol. The alkylation product is also generally free oflight gases generated by methanol decomposition to ethylene and otherolefins. In some embodiments, the organic component of the alkylationproduct may contain at least 80 wt % xylenes and paraxylene may make upat least 35 wt % of the xylene fraction.

After separation of the water, the alkylation product may be fed to aseparation section, such as one or more distillation columns, to recoverthe xylenes and separate the benzene and toluene from the C₉₊ aromatichydrocarbon by-products. The resulting benzene and toluene may berecycled to the alkylation reaction zone, while C₉₊ aromatics can berecovered for blending into the gasoline pool or transalkylated withadditional benzene and/or toluene to make additional xylenes. Oxygenateby-products may be removed from the alkylation product by any meansknown in the art, such as adsorption as described in U.S. Pat. Nos.9,012,711, 9,434,661, and 9,205,401; caustic wash as described in U.S.Pat. No. 9,294,962; crystallization as disclosed in U.S. Pat. Nos.8,252,967, 8,507,744, and 8,981,171; and conversion to ketones asdescribed in U.S. Patent Publication Nos. 2016/0115094 and 2016/0115103.

The xylenes recovered from the alkylation product and any downstream C₉₊transalkylation process may be sent to a paraxylene production loop. Thelatter comprises paraxylene separation section, where paraxylene isconventionally separated by adsorption or crystallization, or acombination of both, and recovered. When paraxylene is separated byadsorption, the adsorbent used preferably contains a zeolite. Typicaladsorbents used include crystalline alumino-silicate zeolites eithernatural or synthetic, such as for example zeolite X, or Y, or mixturesthereof. These zeolites are preferably exchanged by cations such asalkali or alkaline earth or rare earth cations. The adsorption column ispreferably a simulated moving bed column (SMB) and a desorbent, such asfor example paradiethylbenzene, paradifluorobenzene, diethylbenzene, ortoluene, or mixtures thereof, is used to recover the selectivelyadsorbed paraxylene. Commercial SMB units that are suitable for use inthe inventive process are PAREX™ or ELUXYL™.

The invention will now be more particularly described with reference tothe following non-limiting Example and the accompany drawings.

Example

An experiment was conducted to investigate the paraxylene selectivity inthe alkylation of toluene with methanol at a temperature of 350° C., apressure of 600 psig (4238 kPa-a) and a WHSV of 3.5 hr⁻¹ based on totalfeed. The feed used during the selectivation procedure consisted of amixture of methanol and toluene in the molar ratio of 1:2. The catalystused in the study is a formulated MCM-49 extrudate (80% zeolite/20%alumina binder). The reaction was carried out in a down flow fixed bedreactor. The liquid product was collected and analyzed by a 6890 AgilentGC. The gas yield was calculated by difference. The results aresummarized in FIGS. 1-3.

FIG. 1 shows the selectivation for paraxylene over the nine day test.For the first four days, paraxylene selectivity was about 25 wt %, butafter 9 days on stream with the higher methanol to toluene ratio of thefeed, the paraxylene selectivity increased to about 43 wt %. It isexpected that the paraxylene selectivity will continue to increase withthe increased methanol to toluene ratio until it reaches at least 40 wt%.

As can be seen from FIG. 2, methanol conversion is essentially 100%. Nomethanol was detected in the product throughout the run. Tolueneconversion is stable over the nine day test. Average toluene conversionis 45%.

Overall xylenes selectivity observed in the experiment is summarized inFIG. 3, from which it will be seen that the average xylene selectivityover the nine day test is at or near 77 wt %. The balance of theproducts is primarily C₉₊ aromatics, with some C₁₀₊ aromatics andbenzene.

All patents, test procedures, and other documents cited herein,including priority documents, are fully incorporated by reference to theextent such disclosure is not inconsistent and for all jurisdictions inwhich such incorporation is permitted.

While the illustrative forms disclosed herein have been described withparticularity, it will be understood that various other modificationswill be apparent to and can be readily made by those skilled in the artwithout departing from the spirit and scope of the disclosure.Accordingly, it is not intended that the scope of the claims appendedhereto be limited to the example and descriptions set forth herein, butrather that the claims be construed as encompassing all the features ofpatentable novelty which reside herein, including all features whichwould be treated as equivalents thereof by those skilled in the art towhich this disclosure pertains.

When numerical lower limits and numerical upper limits are listedherein, ranges from any lower limit to any upper limit are contemplated.

1. A process for producing paraxylene, the process comprising: (a)contacting an aromatic hydrocarbon feed comprising benzene and/ortoluene with an alkylating reagent comprising methanol and/or dimethylether in at least one alkylation reaction zone in the presence of analkylation catalyst comprising a molecular sieve having a ConstraintIndex less than 5 and under alkylation conditions comprising atemperature less than 500° C. to produce an alkylated aromatic productcomprising xylenes, wherein the molar ratio of the alkylating reagent tobenzene and/or toluene of at least 1:4 is used at least until a targetparaxylene selectivity is achieved; and (b) recovering paraxylene fromthe alkylated aromatic product.
 2. The process of claim 1, wherein thetarget paraxylene selectivity comprises at least 35 wt % of paraxylene,based on the total amount of xylenes.
 3. The process of claim 1, whereinthe molar ratio of the alkylating reagent to benzene and/or toluene is1:2.
 4. The process of claim 3, wherein the aromatic hydrocarbon feedcomprises toluene.
 5. The process of claim 4, wherein the aromatichydrocarbon feed comprises at least 90 wt % toluene.
 6. The process ofclaim 5, wherein the alkylating reagent comprises methanol.
 7. Theprocess of claim 6, wherein the alkylation conditions comprise atemperature of at least 250° C.
 8. The process of claim 7, wherein thealkylation conditions comprise a temperature from 300° C. to 450° C. 9.The process of claim 8, wherein the alkylation conditions comprise apressure from 700 kPa-a to 7000 kPa-a.
 10. The process of claim 9,wherein the alkylation conditions comprise a weight hourly spacevelocity based on the aromatic hydrocarbon feed of 50 to 0.5 hr⁻¹. 11.The process of claim 10, wherein the alkylated aromatic productcomprises at least 70 wt % xylenes.
 12. The process of claim 11, whereinthe alkylation catalyst comprises at least one molecular sieve of theMWW framework structure.
 13. The process of claim 12, wherein thealkylation catalyst comprises at least one molecular sieve selected fromthe group consisting of MCM-22, PSH-3, SSZ-25, ERB-1, ITQ-1, ITQ-2,MCM-36, MCM-49, MCM-56, EMM-10, EMM-12, EMM-13, UZM-8, UZM-8HS, UZM-37,MIT-1, and mixtures thereof.
 14. The process of claim 13, wherein thealkylation catalyst comprises MCM-49.
 15. A process for selectivating analkylation catalyst for the alkylation of benzene and/or toluene with analkylating agent comprising methanol and/or dimethyl ether, the processcomprising: (a) providing an alkylation catalyst comprising a molecularsieve having a Constraint Index less than 5 in at least one alkylationreaction zone; (b) contacting the alkylation catalyst with an aromatichydrocarbon feed comprising benzene and/or toluene with an alkylatingreagent comprising methanol under alkylation conditions comprising atemperature from about 250° C. to less than about 500° C. to produce analkylated aromatic product comprising xylenes, wherein at least a 1:4molar ratio of alkylating reagent to benzene and/or toluene in thearomatic hydrocarbon feed is used until a target paraxylene selectivityis achieved; and (c) recovering paraxylene from the alkylated aromaticproduct.
 16. The process of claim 15, wherein the target paraxyleneselectivity comprises at least 35 wt % of paraxylene, based on the totalamount of xylenes.
 17. The process of claim 15, wherein the molar ratioof the alkylating reagent to benzene and/or toluene is 1:2.
 18. Theprocess of claim 17, wherein the aromatic hydrocarbon feed comprises atleast 90 wt % toluene.
 19. The process of claim 18, wherein thealkylation conditions comprise a temperature from 300° C. to 450° C. 20.The process of claim 19, wherein the alkylation conditions comprise apressure from 700 kPa-a to 7000 kPa-a.
 21. The process of claim 20,wherein the alkylation conditions comprise a weight hourly spacevelocity based on the aromatic hydrocarbon feed of 50 to 0.5 hr⁻¹. 22.The process of claim 21, wherein the alkylated aromatic productcomprises at least 70 wt % xylenes.
 23. The process of claim 22, whereinthe alkylation catalyst comprises at least one molecular sieve selectedfrom the group consisting of MCM-22, PSH-3, SSZ-25, ERB-1, ITQ-1, ITQ-2,MCM-36, MCM-49, MCM-56, EMM-10, EMM-12, EMM-13, UZM-8, UZM-8HS, UZM-37,MIT-1, and mixtures thereof.
 24. The process of claim 23, wherein thealkylation catalyst comprises MCM-49.